This invention relates to a vacuum sealing system for use in the continuous vacuum deposition of thin films on an elongated substrate such as metal strips.
This invention pertains to the maintenance of a high vacuum, of about 10.sup.-6 torr, used in the coating of an elongated substrate such as metal strips. The invention is not limited to a metal strip as the substrate being coated may be of other material. The deposition can be accomplished by such means as, vacuum deposition using an electron beam gun, sputter coating, or any other suitable method which requires a high vacuum.
The production and maintenance of this very low vacuum necessary in these processes is time consuming and expensive. The pumping apparatus must remove several sources of gas in order to maintain the vacuum. As the coating materials are consumed, they liberate gas that must be removed by the vacuum pumps. Outgassing of the substrate and the apparatus' structural materials can pose a significant source of gas which must be removed. Additionally, gasses that leak into the system must be removed.
The high vacuum is required to ensure a uniform and even coating with little impurities. The high vacuum ensures that the molecules travel in a straight line from their source, thereby allowing accurate control and uniformity of the coating. The vacuum also reduces the likelihood of chemical reactions, such as oxidation, occurring between the coating substance and the atmospheric gases.
The problem is further complicated where it is desired to employ a continuous deposition process for metal strips moving through the high vacuum deposition station. In these types of system the gasses from leakage into the system may be significant and complex dynamic seals usually must be used to obtain an acceptable vacuum. Heretofore, for continuous strip deposition there have been a large number of vacuum chambers or areas between seals in order to isolate the very high vacuum chamber at which the deposition occurs.
These prior apparatus utilized a large number of vacuum stages connected in series and the stages are evacuated using large capacity vacuum pumps to establish and maintain the vacuum. U.S. Pat. No. 2,907,679 by H. R. Smith, Jr. discloses the coating of continuous metal sheet with an adherent layer, and uses a several vacuum chambers connected in series, each connected to a large capacity vacuum pump. These systems were difficult and costly to operate at the high vacuum necessary, due to the difficulty of properly sealing the substrate without damaging it and the cost of operating and maintaining the vacuum pumps and the apparatus. In particular, the time required to reestablish the vacuum after replacing the supply of substrate substantially increased the cost of such coatings. The expense involved in changing the substrate, prevented specialty products utilizing unique substrate from being commercially feasible.
The currently disclosed invention solves the above problems and contains advantages over the prior art that will be evident to one skilled in the art. The invention has the advantage of providing a vacuum evacuated container in which to store the newly formed product; this aids in reducing corrosion of the newly formed product. The coated substrate can therefore be safely stored for later application of a protective coating or other treatment.
In general, the object of the device is to provide a new and improved apparatus and method for feeding and sealing with strips or webs that receive a continuous vacuum deposition of thin films thereon.